nrf5340 schematic variations

[mej7000]

In the reference layouts for the nrf5340 there are four variations. I can see the subtle variations in each, but don't know I why would choose 1 vs 2 vs 3 vs 4...  Is there a document which describes the merits of each of the four options? 

nsscprodmedia.blob.core.windows.net/.../nrf5340-xxaa-reference-layout-1_2.zip

The reasoning for not using a ready-made module:
We are creating a device requiring strict consistency over time (requiring an oscillator with low (<3)ppm?), essentially creating a high quality stopwatch, which maintains accurate time in both active and sleep states. We will have a number of these devices that will initially sync their clocks and it's important that they don't excessively drift, without constant "re-syncing".

Therefore we believe we need to have control over the oscillator hardware. However, I am open to alternative ideas if the idea is incorrect.

We initially anticipated using a module, but the 32Mhz clock is always integrated. We could find modules without 32.768khz clocks already in place.

These devices are all monitoring sensors and each device will report it's own time, but each device's time must in sync with the others.

Client insists that each device have it's own internal clock as opposed to a parent device that gets a flag from the children. Communication between devices is wireless/shockburst

[mathiaso]

Hi, Jordan.

In the reference layouts for the nrf5340 there are four variations. I can see the subtle variations in each, but don't know I why would choose 1 vs 2 vs 3 vs 4...  Is there a document which describes the merits of each of the four options?

In the reference circuitry section of the nRF5340 Product Specification, you find two tables describing the features of the different circuit configurations. The different configurations can be freely combined to include the features you need.

If you want control over the crystal tolerance used in the hardware I agree that it might be a good idea to create a design from scratch rather than using a module.

Best regards,
Mathias

[mej7000]

Thanks! That is excellent and exactly what I was looking for!

I should have asked this question too... I am planning to use npm1300 and employ buck1 at 1v8 to drive the nrf5340 and buck2 at 3v0 to drive leds, sensor, buzzer, etc. I plan to configure (at least) PWM, BLE, Shockburst.

I won't be using USB, NFC, or powering anything through the nrf5340 VDD/VDDH

After required functionality is satisfied, the lowest power consumption variation (if that factors in to the four variations) would be my primary objective. After lowest power, easiest & lowest cost to implement would be the next objective.

Just knowing those objectives, does any one of the four variations stand out as the best? After reviewing the four variations, it looks to me like any one of them would satisfy my requirements, but I might be missing something...

[mathiaso]

mej7000 said:

Thanks! That is excellent and exactly what I was looking for!

Wonderful! You're welcome. :)

mej7000 said:

I won't be using USB, NFC

All of the combinations can, as mentioned earlier, be combined freely. Thus, you can leave out the things you see are only present in the configurations including USB and NFC.

mej7000 said:

powering anything through the nrf5340 VDD/VDDH

Could you elaborate a bit on what you mean by this?

mej7000 said:

After required functionality is satisfied, the lowest power consumption variation (if that factors in to the four variations) would be my primary objective.

If power consumption is a priority it is at least advisable to use the DC/DC regulators, as explained here. I guess you've maybe already read this, as you mentioned the buck regulators earlier.

[mej7000]

powering anything through the nrf5340 VDD/VDDH... Could you elaborate a bit on what you mean by this?

This is what I was referring to:

"External circuitry supply

In high voltage mode, the output from VREGH can be used to supply external circuitry from the VDD pin.

As illustrated in High voltage mode, external circuitry can be powered from the VDD pin"

My thought (which may be wrong) is to use the npm1300 buck1 to power nrf5340 VDD and buck2 to power the rest of the circuit (as opposed to the rest of the circuit running off buck1/VDD). I don't know if it's a good idea to separate the power like that, but it appears that is what the npm1300 is designed to do? I'm not 100% sure that's true, so I welcome feedback or alternative suggestions.

To help clarify, here is the initial schematic ideas. Page 1 & 2 are the nrf5340 and npm1300. The other pages are just things I am considering.

edit: Maybe I misunderstood... Are you saying that the addition of the 10uH/1uF inductor/capacitor pair on DCCD/DECD, DCC/DECR, and VCCH/VDD(2.2uf) sets the DC/DC mode and without them I am in LDO mode? Therefore I should add the 10uH/1uF(2.2uF) to get the lowest power consumption?

rapid2.pdf

[mathiaso]

mej7000 said:

This is what I was referring to:

"External circuitry supply

In high voltage mode, the output from VREGH can be used to supply external circuitry from the VDD pin.

As illustrated in High voltage mode, external circuitry can be powered from the VDD pin"

Understood.

mej7000 said:

My thought (which may be wrong) is to use the npm1300 buck1 to power nrf5340 VDD and buck2 to power the rest of the circuit (as opposed to the rest of the circuit running off buck1/VDD). I don't know if it's a good idea to separate the power like that, but it appears that is what the npm1300 is designed to do? I'm not 100% sure that's true, so I welcome feedback or alternative suggestions.

That should work. Just remember that everything communicating with the nRF5340, e.g., sensors, external flash, etc., has to have the same voltage as the nRF5340. Thus, if you have different voltages from the two bucks, the things communicating with the nRF5340 have to be supplied by the same buck as the nRF5340.

mej7000 said:

10uH/1uF inductor/capacitor pair on DCCD/DECD

Enables the DC/DC main regulator.

mej7000 said:

DCC/DECR

Enables the DC/DC radio regulator.

mej7000 said:

VCCH/VDD(2.2uf)

Enables the DC/DC high voltage regulator.

mej7000 said:

and without them I am in LDO mode?

Yes.

mej7000 said:

Therefore I should add the 10uH/1uF(2.2uF) to get the lowest power consumption?

Correct. Although, it is up to you if you are going to use the high voltage mode or not.

[mej7000]

mathiaso said:

That should work. Just remember that everything communicating with the nRF5340, e.g., sensors, external flash, etc., has to have the same voltage as the nRF5340. Thus, if you have different voltages from the two bucks, the things communicating with the nRF5340 have to be supplied by the same buck as the nRF5340.

Thanks! This is huge, because no, I hadn't thought that all the way through! I will run everything off of Buck1 at 3v0. My understanding is that 3v0 will give me lower power consumption on the 5340 than a lower voltage would, which makes sense. All the other components on the PCB will run on 3v0.

Thanks for breaking out what each induction pair does! I didn't realize how that worked although now that I reread that section it makes sense.

mathiaso said:

Correct. Although, it is up to you if you are going to use the high voltage mode or not.

Since I am regulating the entire circuit to 3v0. I seem to have the option to use Normal or High Voltage mode. Can you see a benefit to using one over the other in this case?

Thanks again!